Thymidylate metabolism is required for producing essential building blocks necessary to replicate DNA in dividing cells and has long been an important therapeutic target for cornerstone cancer drugs. Drugs targeting this pathway such as 5-fluorouracil (5-FU) inhibit the enzyme thymidylate synthase (TS) and are currently critical standard-of care therapies. TS-targeted agents are used for the treatment of a variety of cancers including colon, gastric, head and neck, breast, lung and blood related malignancies among others. Grem, J. L., 5-Fluorouracil plus leucovorin in cancer therapy, in Principals and Practice of Oncology Update Series, J. De Vita, V. T., S. Hellman, and A. Rosenberg, Editors. 1988, J. B. Lippincott: Philadelphia, Pa.
There are two classes of drugs that target the TS enzyme: the fluoropyrimidines and the antifolates. The fluoropyrimidines, 5-FU, S-1 and capecitabine (Xeloda®), have wide use in the treatment of gastrointestinal and breast cancers, while the antifolate pemetrexed (Alimta®) is currently used for the treatment of non-small cell lung cancer (NSCLC). Since the discovery of 5-FU over fifty years ago by Charles Heidelberger, the fluoropyrimidines remain one of the most common and effective anticancer cancer drugs used worldwide. Due to this fact, there is an abundance of clinical experience and insight into the mechanism of action of these agents.
The TS inhibitor 5-fluorouracil (5 FU) remains the foundation of many first and second line regimens in the treatment of colon cancer. Single agent therapies including oxaliplatin, irinotecan, Erbitux and Avastin, demonstrate lowered activity in colon cancer compared to 5-FU. In addition to colon cancer, TS-inhibitory agents have demonstrated efficacy in several other solid tumor types. Standard of care now incorporates 5-FU as the backbone drug in combination with oxaliplatin or irinotecan or another agent.
Deoxyuridine triphosphatase (“dUTPase”) is a ubiquitous enzyme that is essential for viability in both prokaryotic and eukaryotic organisms; as the main regulator of dUTP pools, the expression of dUTPase could have profound effects on the utility of chemotherapeutics that inhibit thymidylate biosynthesis. Normally, dUTPase mediates a protective role by limiting the expansion of dUTP pools and countering the cytotoxic effect of uracil misincorporation. According to this model, elevated levels of dUTPase could prevent TS inhibitor-induced dUTP accumulation and induce drug resistance. It has been shown that dUTPase over expression results in a significant decrease in dUTP accumulation and increased resistance to drug treatment when compared to controls.
Chemotherapeutic agents that target de novo thymidylate metabolism are critical for the treatment of a variety of solid tumors, however clinical efficacy is often hindered by drug resistance. Because resistance to these agents is a common occurrence, the identification and exploitation of novel determinants of drug sensitivity within this pathway of proven therapeutic utility is important. As disclosed by Ladner et al. in U.S. Patent Publ. No. US 2011/0212467, the dUTPase enzyme and the uracil-DNA misincorporation pathway can play a driving role in mediating cytotoxicity to TS-directed chemotherapies.
For example, nearly half of cancer patients do not benefit from 5-FU-based treatment due to intrinsic or acquired drug resistance. Due to this fact, there is a critical need to overcome the fundamental challenge of drug resistance and provide new therapeutic strategies to improve patient outcome. This disclosure satisfies this need and provides related advantages as well.